Rain sensors are known which detect the presence of raindrops on the windscreen of a motor vehicle and therefore make possible an automatic activation of the windscreen wipers. Mounting on the windscreen constitutes a problem here, because no reflections must occur between the sensor element and the windscreen. A gap, and equally an adhesive layer, are therefore to be avoided on the optical path.
It is known to stick a holding frame to the windscreen and to fasten the sensor element, which is incorporated into a housing part, to the holding frame by means of a holding device so that the housing part is pressed with the sensor element onto the windscreen. The holding device is constructed for example as a spring which engages over the housing part and has to be pressed under grooves. It is known in addition to push two laterally mounted springs under projecting pins. The springs must provide the engagement and apply the tension at the same time.